Automatic traffic control



April 1960 J. w. SODERBERG 2,933,716

AUTCMATIC TRAFFIC CONTROL Filed Jan. 22, 1957 1 I 6 Sheets-Sheet 1 z 9 a i-x, $85 (92 z 8 8 S2 LL 2?? (OI-\J. l N 2 INVENTOR JOHN W. SODERBERG ATTO RN EY '5 6 Sheets-Sheet 3 ii mmmmozu J. W. SODERBERG AUTOMATIC TRAFFIC CONTROL tutu-O10 A ril 19, 1960 Filed Jan. 22, 1957 mummam EEEJLSE INVENTOR JOHN w. SODERBERG BY r M, "/4 ATTORNEYS CUDE w QE 6 Sheets-Sheet 4 BY an,

April 19, 1960 J. w. SODERBEYRG AUTOMATIC TRAFFIC CONTROL Filed Jan. 22, 1957 FIG. IO

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j W i INVENTOR JOHN W.SODERBERG ma/W'- f I ATTORNE S A ril 19, 1960 J. W. SODERBERG AUTQMA'I 'IC TRAFFIC CONTROL" 6 Sheets-Sheet 5 Filed Jan. 22, 1957 mmmmozo INVENTOR JOHN W, SODERBERG twat-0 N. am

02 CHO I BY ' ATTORNEYS April 19, 1960 J. w. SODERBEBG AUTOMATIC TRAFFIC CONTROL 'Filed Jan. 22, 1957 6 Sheets-Sheet 6 no. -l il mu-N INVENTOR' M JOHN-W. SOQERBERG 1 BY w l M ATTORNEY:

7 2,933,716 AUTOMATIC TRAFFIC coNTRoL Application January 22, 1957, Serial No. 635,318 6 Claims. c1. 340-40 The present invention relates to improvements in the automatic control of vehicular traffic, and more particularly, to improved method and apparatus for controlling the flow of vehicular traflic on highways and the like in accordance with realistic trafiic flow criteria.

In connection with the control of vehicular trafiic flow at a highway junction, or on a multiple lane highway, for example, it has been heretofore proposed to detect the number and rate of passage of vehicles over certain of the highways or highway lanes and to direct the flow of trafiic in accordance with determinations thus made, by means of automatic control circuitry. Improved arrangements for this purpose are described and claimed in the co-pending application of John F. Kearney and John W. Soderberg, SerialNo. 587,304; filed May 25, 1956.

While the invention described in the Kearney et al. application is entirely satisfactory for its intended uses, it is not sufficiently comprehensive to be utilized with complete satisfaction in certain complex multi-highway and multi-lane highwaysystems. Accordingly, the present invention provides improved arrangements for auto matically controlling the flow of trafiic, by means of which a number of complex factors affecting trafiic flow are taken into consideration, and the traflic is directed in a a manner utilizing the highway facilities to greatest advantage and with maximum safety.

In accordance with the invention, the control of vehicular movement is based on factors realistically reflecting actual trailic conditions "at one or more points, so that corrective action is taken, automatically, to'prevent undesirable or unsafe conditions, or to quickly remedy such undesirable conditions as may arise from time to r time. More specifically, the invention provides a control system in which factors such as the number of vehicles moving in a particular flow path and the speed of movement of the vehicles are automatically determined and interrelated in a manner reflecting conditions of traflic congestion, and corrective control of the trafiic flow is carried out automatically, in accordance with the thus determined congestion conditions. Thus, in certain cases, a large number of vehicles may be moving in a particular flow path without creating congestion,

in the sense that trafiic flow would be impaired or arrangements whereby the factors of vehicle movement and speed are interrelatedjon-a continuous basis, with reference to time, to provide an indication of trafiic congestion in a form usable for automatically controlling trafiic directive indicia. Inaccordance with the inven- 2,933,716 Patented Apr. 19, 1960 tion, the average number of vehicles moving past a measuring point is effectively interrelated or integrated with the average speed of the vehicles in a manner refleeting the actual trafiic flow conditions at such point and/or the effect of the conditions at that point on another point in the traific flow path.

Another important specific feature of the invention resides in the provision of integrated control arrangements by'means of which traflic conditions at a plurality of points may be determined and interrelated to provide an indication of the effect of such traflic conditions at another point as, for example, an intersection of highways or division of highway lanes located in advance of the measuring points. Existing traffic control devices with which I am familiar are all actuated by the traffic in the immediate vicinity of the control point, or points, and consequently are able to sense an undesirable situation only after its occurrence; corrective action is then necessary to alleviate the undesirable condition. However, in accordance with this invention, through the use of a multiplicity of remotely located measuring points, particularly on feeder routes, means are provided to initiate anticipatory corrective measures before critical situations arise, thus minimizing or eliminating their effects.

Advantageously, trafiic control in accordance with the invention is carried out with electronic equipment arranged to receive various indicia of traflic conditions and to actuate trafiic directive means in accordance therewith. However, it is contemplated that other means, such as mechanical devices, may be employed in the same or an equivalent manner. Accordingly, the invention, as hereinafter described with more particularity, is considered as residing in the method of control, as well as in the improved apparatus used for carrying out the new method. v v

For a better understanding of the invention, reference should be made to the following description and accompaning drawings, in which:

. Fig. 1 is a simplified plan view of a complex highway system incorporating the traflic control means of the invention;

Fig.2 is a perspective view of a trafiic directive sign which maybe employed inthe new control system;

' Fig. 3 is a fragmentary perspective view of a multilane highway, with a traflic directive sign, which maybe advantageously employed in the new system;

Fig. 4 is a schematic representation of a highway lane, with trafiic detecting and evaluating means of the in venticn associated therewith;

Fig. 5 is a schematic representation of a complex control arrangement incorporated in the new traific control system for evaluating andtranslating .traffic flow factors;

Figs. 6-10, inclusive, are schematic representations of various of the circuit elements employed in the control arrangement of Fig. 5;

Fig. llis a simplified plan view of a highway intersection at which control means in accordance with the invention are utilized for regulating trafiic flow; and Figs. 12-13 are schematic representations of control circuit means employed in connection with a trafiic control system for use at a highway intersection, such as that shown in'Fig. l1. j

Every highway or highwaysystem is designed for, or in fact has, a practical capacity for handling trafiic, at which eliicient use is made of the highway. Stated in another way, a highway may be most efiiciently used when the traflic congestion is at a certain value. The"prcferred congestion value may be determined by surveys or in some cases by calculation.

In order to reflect the extent of use of a highway or 3 e h r flow p rl d n as cnsl uti izt a onge ion index, based upon the equation where I is the congestion index, N is the actual numher of vehicles per unit distance, S is the actual average speed of the vehicles, N and S are normal or preferred values of N and S and a and b are weighting constants reflecting the relative effects of vehicle density and speed. The constants a and b may be such that, numerically, the congestion index is one, when N equals N and S equals S A. d i a ion o the b v q a n the u estion uthxre uit n he equat on.

l=dt(a"P+b') wheel s h c n estion. index, d. .s.t. 1-. me r uires ta archi h o mo t een o fixedro nts, P s number 0.5 ehi e a n m r ng po n n a Unit a timess l an r s wn a saccordance with the invention, the congestion in- I' is determined at one or more points in a highway or' highway system and is reflected in the form of an electrical voltage value, for example, whereby trafiic directive indicia may be controlled in accordance with prevailing congestion indices, in order to effect corrective or preventative control of the traffic flow.

Referring now to the drawing and initially to Fig. 1 thereof, the numeral 1% designates a highway intersection at which a multi-lane highway 11 joins with a second highway 12. In the illustrated highway system, the highways 11, 12 rejoin at a second intersection 13, so that, in elfect, the highways 11, 12 form alternate routes. Also, in the illustrated system, a cross highway 14 intersects both the primary highways 11, 12, and feeder highways 15, 16 intersect the highways 11, 12, respectively. It will b derst of c ur e. that h de ibe h a system is merely illustrative, and is not to be considered as imposing any limitation on the invention.

in the illustrated system, the flow of trafiic moving from left to right in Fig. 1 is subject to automatic control, in accordance with the invention, to the end that traffic congestion at. points along the primary highways 11, 12 is determined and interrelated. The congestion indicia is then translated into a usable form, whereby a trafiic directive sign 17, of the type shown in Fig, 2, for example, may be appropriately energized to direct vehicles appr achi g he nter i n nto one q he th r o the highways 11 or 12. In accordance with the inventi n tt fi n est n i me u e t. a numb r f P n inc ud n po n a ent o h cross nd eeds thigh: ways 14-16, whereby the effect of vehicular movements to and from such highways is taken account of, and the plurality of congestion determinations are interrelated to reflect the relative effect thereof at the intersection 19. The sign 17, positioned ahead of the intersection 10, is then automatically energized to present trafiic-directive indicia for directing the flow of trafiic onto a desired one of the alternate highways 11, 12.

In the system of Fig. 1, trafic congestion along the principal highway 11 is measured at a plurality of points 182 2, the measurements at each point being made in each-of the several lanes provided for trafiic moving from leftto right. Congestion is also measured at points 1542- 152 on the cross and feeder highways 14, 15, in the lanes thereof feeding trafiic onto the main highway 11. In a similar manner, congestion is measured at a plurality of points 23-27 along the alternate highway 12 and at points, not specifically indicated, along lanes of highways 14, 16 feeding traflic onto the alternate highway 12. In accordance with one form of the invention, the separate congestion measurements, taken at the several points on each highway, are weighted in accordance with the efiect ofcongestion at the respective points on the flow o t a f a er s he. mai n lt r ig 1. 1

and at or near'the intersection 10. The weighted values for each of the highways 11, 12 and its feeders are added, providing, for each highway, an indication of traffic congestion or anticipated congestion throughout a portion of its length, in terms of its effect at or near the intersection. The added measurements are automatically compared, and the traflic directive sign 17 is energized accordingly, to direct trafiic onto the highway best adapted, at the time, to receive it.

In order to determine trafirc congestion at a particular point on a highway, an apparatus of the type shown in Fig. 4 may be advantageously employed. The apparatus comprises means such as trip plates 28, 29 set in a highway lane to detect both the number and speed of vehicles passing thereover. It is contemplated, of course, that other conventional trafiic detecting devices, such as phptciest s csllsq heike a s for t a pss; 24 ad sn as n he a. ai of spaced 'd es er re us d, h r a e ap rt a distance such that one vehicle is registered by both detectors before a following vehicle begins to pass the detecting point.

In the preferred form of the invention, the trip plates 28, 29 constitute part of an electrical circuit leading to a congestion index computer 30, which is arranged to process signals, provided by passing vehicles, in a'mannot such as to provide an electrical signal representative of the congestion index I, mentioned hereinbefore.

Referring now to Fig. 6, the congestion index computer 3,0 includes a gaseous discharge valve 31, such as a conventional thyratron, which has an anode-cathode circuit comprising a source of direct current voltage and a normally closed switch 29a, actuated by the trip plate 2 9 placed second in the line of traffic flow. The control grid circuit for the valve 31 includes a source 32 of ne a ve bias i h normall mai a n h valve n a QIhQ BQUG iB cqnsii iony a d a a ut 3 o positive a id potent al 9--.. t .iss th ss imsll n s ts lfia s a. .tlh h r t t i pla e hen. a. ehi le P$ o e thev st ate s t h 2851 is momentarily closed and negative grid bias on the vaive 3 1 is overcome. Conductionis thereupon initiated in the valve 31 establishing a voltage across cathode resistor 34. Conduction in the valve continues, even sit s t h 4: s eo ened, ti h i passes Over he. se nd r p. pl te 2.9 a tu t ng i h2 4 t m na ly. 99. the mimic-c th de ir ui 9 the valve hi e Passin q h ri pla e at sivsas ssd. will. c us wud tic a h? v .1 for a en th. tim dz ni du ins vq t sc Pu s 9 p ede e m ned. ma ni ude an 2 urat on al. to us qrmsti st ated a a s-fi) iS if .d. i1 a ci uit .6.. 9 re a e. a s arp nosi i" p ke ndicated at rk n e ad n ed d h Pulse,

The. positive. spike 37 is used to trigger a one-cycle multiv brat e ou p t Of.- which is a Single P llndic e a 3. onstan m lit de a d f a duration much less than the shortest anticipated pulse 35.

Advantageously, the duration and/or amplitude of the pulse 32 is the function of an adjustable constant, which, in, terms of the derived equation n 1ent ioned before, is ela d o. qq tsiit 3 e, o t o t vihrator 38; is then passed through a buffer circuit 40, in h. he u s is u e im ose output bias voltage representative of the constant b.

Each pulse from the output of the buffer circuit 40 is passed through an integrating circuit 41 which provicles an output voltage proportioned to aP+b' in terms of the beforernentioned equation. The integrator voltage output is then applied'to a buffer-amplifier 42, the output voltage signal thereof being fed to a chopper 43, which converts the signal into square waves at a reft m fr u nc advan a e u atj60. cl Pe P 1d- The small arrows to the circuits 38, 40, 43, in Fig. 6,

represent reference voltagesused in regulating the operadoubt the respective circuits.

The square-wave output of the chopper 43 is compared with a reference potential at potentiometer 44, and a servo-motor 45 is energized in accordance with the,.diilerential, if any, to adjust. the arm of the potentiometer 44 and also the arm of a second potentiometer Each pulse from the valve 31 is also fed .to a butleramplifier 47, and then to an integrating circuit 48, the output of which is proportioned to'the average value of dt. This output voltage is, in turn, fed to a second buffer-amplifier 49, and the output of the amplifier is.

applied to the terminals of the servo-adjusted potentiometer 46. I

Output leads 50, from the servo-adjusted potentiometer 46 are thus at a potential difference determined by a .voltage value (across the potentiometer 46) representing cit and a potentiometer setting representing (a'P+b'), in terms of the beforementioned equation. The output voltage at the leads 59 thus represents-dr(a'P+b), which also represents the congestion index, I, sought to be determined.

As thus determined, the congestionindex may be utilized in a variety of ways to effectuate desired traffic flow control. In the specific arrangement of Fig. 1, congestion index computers are provided at or in association with each of the measuring points 18-27, 150-152 and a control circuit of the type illustrated schematically in Fig. 5 may be employed. Thus, in Fig. 5, pairs of congestion index computers such as 54, 55-56, 57 are provided for the measuring points 18-22 on dual lane highway 11, computers 51-53 are provided for the measuring points 156-152 on the feeder and cross highways, and computers 58-69 are provided for each of the measuring points 23-27 on highway 12.

Output signals from the pairs of 54, 55-56, 57 computers for highway 11 are fed into separate weighting circuits such as indicated at 64, 70, to be described,

-where the separate signals are modified to reflect the anticipated effect at one point of congestion at the measured points, i.e., in the specific example of Fig." 1, the eifect at the intersection of congestion at the respective measuring points 18-22. Likewise, signalsrfrom the computers 51-53, for the highway lanes feeding the main highway 13. (points 150-152), are fed to weighting circuits 61-63, which modifythe signals to reflect the anticipated congestion to be caused by the feeder traffic. The weighting circuits may be adjusted on the basis of trafiic surveys, for example, on an approximation may be made by adjusting the weighting circuits so that the measurements made at points closer to the intersection weigh more heavily in the final deter-' mination.

A simplified form of weighting circuit is illustrated in Fig. 7, as comprising a potentiometer, across the end terminals of which is applied the congestion index signal from a congestion index computer. An adjustable element 66 is used for regulating the position of the potentiometer arm 65a, whereby a predetermined portion of the computed congestion index signal is applied to the output leads 67 of the potentiometer;

' Weighted congestion index signals from the respective weighting circuits 61-63 and 64, 70 are. directed to a summing circuit 68 (Fig. 5), by means of which a voltage signal, representing a summation of the respective weighted signals, is applied across a resistor 69 (Fig. 9).

that the respective signalup'otentials are-applied thereto with opposite 'polaritie's 'The ungrounded'terminals of the resistor are connected to each other at a terminal point 77, through resistors 78, 78 forming a balance circuit 79 (Fig. 5). The arrangement is such that if the summation signal voltages across the respective resistors 69, 75 are equal, point 77 will be at zero potential, with respect to ground. However, if the voltages are unbalanced, point 77 will assume a positive or negative potential with respect to ground, depending upon which of the resistors 69, 75 has the greater potential drop.

As shown in Fig. 9, the terminal point 77 is connected in the control grid circuit of a gaseous discharge valve 80. The valve 80 has ananode-cathode circuit including a relay 81 and a source of A.C. voltage 82, whereby the valve is caused to conduct on alternate halfcycles, when the grid potential is within a predetermined range. r

The control grid circuit for the valve. 30 includes an A.C. source of negative bias, including a biasresistor 83, and a potentiometer. 84 connected to the terminal point 77. The grid bias is such that the valve is normally non-conductive. However, when the terminal point 77 turns suflicienlly positive, with respect to ground, the valve will be caused to conduct during alternate half cycles to energize the relay 81 and close the contacts 81a thereof. A capacitor 810 maintains the energization of the relay during non-conducting half cycles.

When the terminal point 77 turns sufficiently negative, conduction is blocked in the valve 80, de-energizing relay 81 and causing contact 81b thereof to close. it will be understood, of course, that the characteristics of the valve 80 are such that the grid signal must be lowered considerably, after conduction has been initiated, in order to block further conduction. This is advantgeous, as will appear, since slight variations in the summation signals will not cause, the valve 80 to oscillateon and on. The hysteresis in the on-otf control of the balance circuit valve 80 may be regulated by adjusting the potentiometer 50 that the sensitivity of the balance circuit may be varied asdesired.

Switch contacts 81a, 81b of the relay 81 are part of a control selector circuit 85 including selector switches 86, 37. The switches 86, 87 are, in turn, connected through a time delay circuit 88 (Fig. 5) to a directional indicator which, for the purpose of this illustration, will be considered as the traflic directive sign 17.

When the relay contact 8112, is closed, as when the negative summation voltage on, for example, the resistor.

75 overbalances the voltage or resistor 69, an arrow on the trafiic directive sign 17 will have one head 17b thereof lighted, directing trafiic onto highway 11. if.

the traflic congestion on the highway 11 and/ on its feeder lanes becomes materially greater than the congestion or anticipated congestion on the highway 12, valve 80 will be rendered conducting, and relay contact 81a will close to light head portion 17c of the arrow 17a, and extinguish head portion 17b. This causes trafiic to be di rected onto highway 12, until such time as thecongestion balance is materially reversed.

Advantageously, when the indicator arrow 17a of trafiic.

directive sign 17 is changed, so that traffic is directed onto a difierent highway, both arrowheads 17b, 17c are lighted simultaneously for a short. period, before the previously lighted head is extinguished, to assure a smooth transition in the flow of traffic. This is accomplished by the time delay circuit 88, shown in part in Fig. 10.

In the illustrated time delay circuit, each arrowhead portion is controlled by a relay, such as relay 8?, having a set of normally closed contacts which complete the energizing circuit for the arrowhead. When the condition of the main selector relay is such that arrowhead 17b, for example, is to be lighted, a circuit is completed through selector switch 87, applying a high negative bias to the grid circuit of a gaseous discharge valve 90,

7 through a rectifier 91. "This maintains 'thevalve "90 '3 non-conductive s't'a'te,so jth'at relay 89is tie-energized the lighting circuit for arrowhead 17b is completed.

When the selector relay 31 is actuated, the bias circuit is opened, and a'grid capacitor 92 begins to discharge through a resistor 93. After apreset time, the grid loses its strong negative potential, and the valve 90 begins'conducting to actuate relay 89 and extinguish the arrowhead 17b. A similar time delay circuit is associated with the opposite arrowhead 170, as will be understood.

In many cases, the control of traffic flow should modified periodically, throughout the day, to accommodate such recurring variables as rush hour trafiic, school hours, etc. Accordingly, circuit means, such as shown in Fig. 8, may be employed whereby factors variable with time are automatically :providedfor. I

In the circut of Fig. 8, the "DC. voltage signal from a congestionindex computer is applied across a potentiometer 94, the movable ar'm'94'a of'whi'ch is adjusted bya motor-driven cam 35, as a function of time. The output of potentiometer 94 maybe applied across the terminals of a second potentiometer '96, the movable arm 96a of which is adjustedby a cam 97 driven by a servomotor 98. The servomotor is acted upon by an A.C. reference potential 99, and by a square wave potential derived from the congestion index voltage signal by means of a chopper 100. The small arrow to the chopper circuit 1% represents a reference voltage used in regulating the operation of the circuit. The contour of the cams Fifi, 97 may be determined empirically, or otherwise, so that the congestion index signals are variably weighted, as a function or" time and of the congestion index, to best suit the specific requirements of a particular installation. In a typical traffic control system, one or more, but not necessarily all of the congestion index computers may be provided with time-variable weighting controls, as at"101'103, in "Fig. 5.

In many cases, it may be desirable to route the several computed congestion index signals to a "remotely located central control station, as in'dicatedat lMinFig. 5, so

fedseparately into a gating circuit "111 (Fig. 12), in'the form of voltage signals, and the gating circuit, which may be 'o'f conventional design, selects the larger otthe voltages and "passes it along as an output signal. In a similar manner, congestion index measurements made on the opposite approaches to the intersection along highway 199 are fed to a second gating circuit 112., which selects the larger voltage value and passes it on as an output voltage.

Congestion index voltage signals from the respective gating circuits 1'11, 112 are fed into choppers 1123, 114, respectively, which convert the signals into square waves at a. reference frequency. The respective square wave signals are thenfed to servoniotors 115, 116, which balance the signals against reference voltage otentiometers 5.37, 'Ihc serv'orriotors 115, 116 operate adjustable arms of potentiometer-s "11* 12% forming part of a bridge network 121, including a fixed resistor 122 and a servodriv'en potentiometer 123.

Operation vof one or both of the servomotors 115, 116 causes the bridge "121 to become unbalanced, and energizes a third servomotor 124, which adjusts the potentiometer 123 until the bridge is again in balance. The servomotor 124 is also connected to a lead screw 125, carrying a cam follower 12s co-acting with a three dimensional cam 127. The cam 1.27 has low and high surfaces which, from one end of the cam to the other, vary in proportion. The arrangement is such that as the cam is rotated at constant speed, by a motor 5.28,

that traific conditions at the separate measuring points survey operation.

As will be readily understood, the 'basic elements of the new control system 'm'aybe applied in a variety of ways, one, specific example being, in the control of traific flow in the sevcrallanes of a'multi-lane highway. Thus,

in Fig. '3, for example, a multi-lanehighway 195, toll gate approach, or the like, is provided with an overhead structure 1&6 bearing 'controllably energizablet'i'atfic directive indicia. In such an installation, the control system may be employed to advise tr-aflic, in advance, of the least congested lane.

In the system of Figs. 11-13 the new control apparatus may be advantageously utilized in the control of tratlic stop-'and-g'o lights at a highway intersection. In the'representative highway intersectionshown inFig. 11, pairs of'traffic' lights 106a, 1061) and 107a, iiiib'ar'e provided at the intersection of highways103,'1l39, highway 108 being a multiple lane highway in the illustration.

Each of the highway lanes leading to the intersection is provided with one or more sets of detectors and cornputors 110, of the type shown in Fig."4,so that congestion indexfmeasurements are made -atone or more points in the flow pathsleading to the intersection.

Congestion-index measurements,'rnade onthe opposite approaches -to"the"iutersection along "highwaydtlti, are

the cam follower 126 is raised during a predetermined portion of each revolution, depending upon the location of the follower, axially, along the cam.

In the illustrated system, the cam follower actuates a switch 129 (Fig. 13), between one or two circuit completing positions, as it moves between high and low portions of the cam 127. When contacts 129a of the switch'129 are initially closed, a circuit is completed to a relay 130, which is advantageously a time delay relay. The initial closingof contacts 129:: also completes a cir cuit through normally closed contacts 13% of the relay 130, to energize the amber light 131 of the traffic signals 107a, 1071). The green light 132 of this signal, and the red light 133 of signal 166 have been energized previously-through a circuit including normally closed contacts 134a of a relay 134.

A predetermined time after energization, the relay actuates, closing contacts 1349b and opening contacts 130a to "the amber light. Closing of contacts 13% complete's a circuit to, and energiz es relay 134, to open contacts 134a thereof and close contacts 13% and 134a. Opening and closing, respectively, of contacts 134a, 13412 extinguishes the redi'and green lights 133, 132 and energizes green andred lights 135, 136, of the signals 106, 107, while closing of contacts 1340 completes a hold-in circuit for relay 134, through normally closed contacts 137a of a relay 1157.

Upon continued rotation of the three dimensional cam 127 the switch 129 is actuated to open contacts 129a and close contacts 1129b thereof. This simultaneously deene'r'gizes 'timedelay relay 130 and energizes a second time delay relay 138. Green and red lights 135, 136 remain on for a period, however, since the relay 134 is held in an energized condition through the circuit including contacts'137a; and, at the same time, amber light "139 is energized through a circuit including normally closed contacts 138a of time delay relay 138.

After a predetermined delay period, relay 138 is actuated, closing contact 13812 thereof and reversing the traffic lights. Thiscycle repeats, being varied only in the respective periods of energization, as determined by the positionofthe cam'follower 126, axially, along the three dimensional cam 127.

The new system provides a new approach to the'problembf-"trafiic 'flow control, whereby traffic congestion, referenced to a-preferred or normal congestion, forms V 9 the basis for directing the flow of traflic. The method and apparatus of the invention is founded on the principal that mere numbers of vehicles on a highway or highway lane does not necessarily render the trafiic condition undesirable. Rather, the number of vehicles, taken together with the average rate of movement thereof, reflects the congestion of the trafiic, and the actual congestion, referenced to a normal or preferred congestion, provides a realistic criterion for directing the flow of traflic in a manner which will effectively prevent or remedy underside traflic conditions, to the extent possible under the circumstances.

In accordance with thenew system, realistic traific control may be applied in va variety of .ways, to divert or regulate the flow of traflic at an intersection, for example, or to direct approaching Vehicles into a relatively uncongested flow path, the foregoing being merely by way of example and not of limitation.

One of the important aspects of the invention resides in the provision of an improved method and system for controlling the flow of vehicular traflic, whereby highway congestion at a point or points is anticipated and reflected before it actually occurs. Accordingly, a certain lead time is provided, in which remedial or corrective action is taken to alleviate the congestion before it actually occurs.

It should be understood, however, that the forms of the invention specifically illustrated and described herein are merely representative.v For example, the specific cir cuitry described herein may be varied substantially in its make-up, or, in some cases mechanical means may be employed. Such variations are considered to be within the capabilities of one skilled in the art and therefore Within the scope of this invention. Accordingly, the scope of the invention should be determined by reference to the following appended claims.

1 claim:

1. Apparatus for controlling the flow of vehicular traflic at a predetermined point in a continuous flow path,

which comprises measuring means at spaced measuring points in said flow path for measuring vehicular congestion at each of said points in said path, means associated with each of said measuring means operative to weight the respective measurements in accordance with the effect, at said predetermined point, of vehicular congestion at the respective measuring points, means to effect a summation of the weighted measurements, and traflic directive indicia positioned in proximity to said predetermined point and operable in accordance with said summation.

2. Apparatus for controlling the flow of tratfic on a highway having one or more feeder lanes, which comprises measuring means located on the highway and on the feeder lines at points in advance of the intersection of said highway and feeder lanes, said measuring means comprising means for detecting the passage or" vehicles and for providing an electrical signal which is a function -of the number of vehicles passing a point in a unit of time and means for determining the speed of the vehicles and providing an electrical signal which is an inverse function of such speed, means for, at least in efiect, multiplying said signals to provide a control signal which is a function of the vehicular congestion level on the highway and feeder lanes, means for, at least in elfect, comparing said control signal with a predetermined congestion level, and means for directing the flow of traflic in accordance with the compared control signal.

a r 3. Apparatus for controlling the flow of vehicular trafi'ic in a flow path, which comprises spaced detecting means actuable upon the passage of a vehicle thereby to detect the passage ,of said vehicle and the speed of movement thereof, first circuit means providing an electrical signal which is a function of the number of vehicles passing said detecting means in a unit of time, second circuit means providing an electrical signal which is an inverse flmction of the speed of vehicles passing said detecting means, means to interrelate the factors of passage and speed thus detected comprising third circuit means for, at least in effect, multiplying said electrical signals to provide a control signal which is a function of vehicular congestion level in the flow path, means for, at least in effect, comparing said control signal with a predetermined congestion level, and tratfic directive means positioned in proximity to said flow path and controlled, at least in part, by said means to interrelate.

4. Apparatus for controlling the flow of traffic at an intersection of highways having a cyclically operable traflic control indicator, which comprises means to meas ure vehicular congestion level on the respective highways, said means comprising first circuit means providing an electrical signal which is a function of the number of vehicles passing a point in a unit of time, second circuit means providing an electrical signal which is an inverse function of the speed of vehicles passing said point, and third circuit means for, at least in efiect, multiplying said electrical signals to provide a control signal the level of which is a function of vehicular congestion on the respective highways and means to vary the operation of said indicator, within its cycle, in accordance with the respective levels of said control signals.

5. Apparatus for controlling the flow of trafiice at an intersection of highways having a cyclically operable traflic control indicator, which comprises means to measure vehicular congestion on the respective highways, said means comprising first circuit means providing an electrical signal which is a function of the number of vehicles passing a point in a unit of time, second circuit means providing an electrical signal which is an inverse function of the speed of vehicles passing said point, and third circuit means for, at least in eifect, multiplying said electrical signals to provivde a control signal which is a function of vehicular congestion on the respective highways, means i to vary the operation of said indicator, within its cycle, in accordance with said control signals, circuit means to compare the vehicular congestion control signals for the respective highways, and means to vary the operation of said indicator in accordance with the comparison.

6. Apparatus for controlling the fiow of traflic on a highway having one or more feeder lanes, which comprises measuring means located on the highway and on the feeder lanes at points in advance of the intersection of said highway and feeder lanes, said measuring means comprising means for detecting the passage of vehicles and for providing an electrical signal which is a function of the number of vehicles passing a point in a unit of time and means for determining the speed of the vehicles and providing an electrical signal which is an inverse function of such speed, means for, at least in effect, multiplying said signals to provide a control signal which is a function of vehicular congestion on the highway and feeder lanes, means for directing the flow of traflic in accordance with said control signal, circuit means for combining said control signals and for providing a further control signal which is a functoin of anticipated congestion at said intersection, and means for directing the flow of traflic in accordance with said further control signal.

References Cited in the file of this patent UNITED STATES PATENTS 1,835,916 Vickery Dec. 8,1931

2,088,723 Preist Aug. 3, 1937 2,126,431 Von Opel Aug. 9, 1938 FOREIGN PATENTS 436,883 Great Britain Oct. 21, 1935 OTHER REFERENCES Publication, The American City, pp. 143 and 145, Sept. 1948. 

